1. Field of the Invention
This invention relates to an apparatus for the connection of control current lines, in particular for withdrawable units in low voltage switchgear.
2. Background Information
Low voltage switchgear, such as motor control centers or power distribution installations, have employed withdrawable unit design for many years, in cases where it is necessary to be able to quickly replace components assembled into a functional unit, to achieve short down times for the electrical operating equipment when maintenance work is required, or to achieve brief operational interruptions caused by defective functional components.
For testing or maintenance purposes, it is currently customary to insert or remove the withdrawable unit into or from a test position, whereby only the load current is interrupted, and the control current to the individual functional components is continued in this position.
The continuation of the control current is achieved by contacting the connecting elements which carry the control current even in the test position.
If the withdrawable unit is pulled out farther, the control current feed is also interrupted. This position is customarily called the disconnected position.
The position in which both the load current and the control current are fed is called the "On" position.
An apparatus of the type described above is disclosed in OS 2515152. In that case, the connecting elements are designed as sliding contacts, which slide over one another from the "On" position to the test position.
In such a case, the connecting elements can suffer wear and damaging abrasion on account of the sliding metal connecting elements.
An additional contact apparatus which is also suitable for the control current connection, is realized by means of a form-fit. Such an apparatus is disclosed in OS 3114837.
The connection designated an overtravel contact consists of a contact finger which is equipped with expanded portions for a positive connection with a contact pin, whereby the connection is released by means of a tripping sleeve.
This type of connection has the disadvantage that it is complex and expensive, and takes up a relatively large amount of space. It is therefore not well suited for a large number of control lines.